Air pollution is an issue that has been discussed for many years. Pollutants in the air have been proved to affect human comfort and health. Originally, most air pollution concern was focussed on such factors as automobile and factory stack emissions. Relatively recently, it has been found that the quality of the air inside a home or business is frequently worse than the quality of the air outside that very same home or business. The problem has been termed the Sick Building syndrome, and it has been proved that many of the symptoms of this syndrome are caused by volatile organic compounds (hereafter VOC) in the ambient air within the building.
This concern with indoor air pollution has passed from the realm of scholarly study into the area of publications intended for the general public. The Environmental Protection Agency published "The Inside Story: A Guide to Indoor Air Quality" in 1988. This booklet discusses, among other things, the health effects caused by indoor air pollutants. The pollutants discussed include various VOCs, especially formaldehyde, as well as particulates.
Any recognized problem breeds potential solutions, and many devices for reduction of air pollution have been developed. The simplest such devices draw the air through some sort of filtration device. Air purification devices to remove particulate materials such as dust and smoke particles from the ambient air particles are well known. Examples are the various versions of small units intended to remove cigarette smoke from the air. Electrostatic precipitation devices produce basically the same results without the need for filter replacement. However, such devices can do little to remove VOCs from the air.
The next step in sophistication are devices that, often in conjunction with a filtration or electrostatic precipitation system, incorporate an adsorptive material such as activated charcoal. The adsorptive material aids in the removal of volatile organic compounds from the air.
One rather multifunctional and complex device includes many air purification approaches: filtering systems including an electrostatic one, adsorbent materials, washing systems, germicidal and heating elements, as well as fans to move air through the device. This device, patented as "Gas Treatment Device", U.S. Pat. No. 3,299,620, to C. E. Hollingworth, is intended to process large volumes of air, either indoors or outdoors.
A device employing a catalyst to purify an air stream is disclosed in U.S. Pat. No. 5,008,091, to Bassi et al., "Method for Purifying Air." This method involves preheating the air and passing it through a catalytic bed which is made up of a combination of platinized heat-conductive pellets and metal turnings. This bed is to be maintained at a temperature between 160.degree. C. and 300.degree. C. Low molecular weight hydrocarbons in the airstream are oxidized during passage through the catalytic bed. An intended use of the device is to remove ethylene from fruit storage chambers, since ethylene is known to hasten the ripening process and is therefore undesirable.
U.S. Pat. No. 4,138,220 to Davies et al., "Apparatus for Catalytic Oxidation of Grease and Fats in Low Temperature Fumes", discloses an apparatus intended to remove odors and other hydrocarbons such as grease, fats and oils from the air stream emitted form a restaurant's cooking operations. A preferred catalytic system utilizes a honey-comb substrate of refractory material coated with a platinum containing catalyst.
The apparatus has a fan which draws air into the essentially cylindrical structure. Inside the structure are baffles and heat exchangers, as well as the catalytic system. An auxiliary heater heats the incoming air stream, which then passes through the catalytic system, where the hydrocarbons are oxidized. Warmer, processed air is directed back from the combustion zone into a heat exchange zone, where it seems to heat incoming air and reduce the need for auxiliary heat. The temperature of the air moving into the combustion chamber is thermostatically controlled and the combustion zone kept at a temperature of 357.degree. F. to 475.degree. F. (181.degree. C. to 246.degree. C.).
U.S. Pat. No. 4,948,567 to Atarashiya, "Deodorizer For Refrigerators Or The Like", discloses a device which has a deodorizing component comprising an adsorbent material (such as activated charcoal or silica) layer and a catalyzer (such as platinum or nickel) layer. The device has heating means which serve to regenerate the adsorbent material. The catalyzer layer is formed on one side of the adsorbent material by dipping the adsorbent layer in the catalyzer solution.
Most currently available air purification devices are thus of either limited utility (the pure filtration systems) or are fairly complicated and are therefore subject to mechanical malfunctions and relatively expensive to produce and thus to purchase.
As discussed before, most residential air purification devices on the market are filtration systems, sometimes incorporating adsorption systems, electrostatic precipitators and negative ion generators.
Ironically, the electronic air cleaners and negative ion generators used in an attempt to purify indoor air themselves produce ozone, since they are high voltage devices (see Indoor Air Pollution by Thad Godish, Lewis Publishers, 1989, at p. 280), and excess ozone is well known to have adverse health effects on humans--urban areas, especially in hot and humid weather, publish ozone alerts recommending limiting outdoor activity. Thus, a simple, relatively inexpensive device with a minimum number of components capable of removing volatile organic compounds from an ambient air space and destroying ozone is highly desirable.